Ballmer was sandwiched in between Microsoft co-founder Bill Gates and current CEO Satya Nadella for the interview.
"I took just enough economics in college — that tariffs are actually going to bring some turmoil," said Ballmer, who was succeeded by Nadella in 2014. Gates, Microsoft's first CEO, convinced Ballmer to join the company in 1980.
Gates, Ballmer and Nadella attended proceedings at Microsoft's Redmond, Washington, campus on Friday to celebrate its first half-century.
Between the tariffs and weak quarterly revenue guidance announced in January, Microsoft's stock is on track for its fifth straight month of declines, which would be the worst stretch since 2009. But the company remains a leader in the PC operating system and productivity software markets, and its partnership with startup OpenAI has led to gains in cloud computing.